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Pleural fluid pH is an important measure for determining the clinical management of pleural diseases. For example, a pleural fluid pH <7.2 in patients with suspected pleural infection should mandate the placement of a chest tube. However, pleural fluid pH might vary based on the techniques used to obtain and test the sample. Using 92 samples from 81 patients, researchers in the U.K. explored the potential effects of time to analysis and of air, lidocaine, or heparin left in the testing syringe.
The presence of air in the syringe increased pleural fluid pH by 0.08 (P<0.001). Residual lidocaine, even at minimal volume, decreased pH (e.g., 0.2 mL of lidocaine lowered pH by 0.15; P<0.001); at larger volumes, the decrease was greater. Retaining t…